What is Fracking and why are people so concerned?

What is fracking? Hydraulic fracturing (fracking) is a technique used to extract hydrocarbons trapped in certain types of rock. In particular the widespread use of fracking is being driven by the expansion in shale gas extraction.; What is shale gas? Shale gas is natural gas that is trapped in impermeable shale rock, as opposed to more conventional natural gas deposits that are trapped below a layer of impermeable rock. Therefore simply drilling down to it is not enough and the rock must also be fractured in order to allow the gas to escape.; How does hydraulic fracturing work? Hydraulic fracturing uses pressurised fluid to free trapped gas. Wells are drilled and the fracking fluid injected into them under high pressure to crack the rock. The fracking fluid consists of water, sand and a massive amount of chemicals. Millions of gallons of water (and hundreds of tons of chemicals) are used to frack a well.; Why should we be concerned about fracking? There is a substantial amount of evidence documenting the side effects of hydraulic fracturing, the majority of which are related to water contamination. The main causes of concern are explained in this pamphlet.